Trisomy 18 syndrome

Trisomy 18 syndrome, also known as Edwards syndrome, is a chromosomal disorder caused by the presence of an extra copy of chromosome 18. It is the second most common autosomal trisomy after Down syndrome (trisomy 21). The condition can occur as full trisomy 18 (most common, accounting for approximately 94% of cases), mosaic trisomy 18, or partial trisomy 18. The ICD-10 codes reflect these subtypes: Q91.0 and Q91.1 for full trisomy 18 (nondisjunction and mosaicism, respectively), Q91.2 for translocation forms, and Q91.3 for unspecified trisomy 18. Trisomy 18 affects virtually every organ system in the body. Key clinical features include severe intrauterine growth restriction, a distinctive craniofacial appearance with a prominent occiput, micrognathia (small jaw), and low-set malformed ears. Characteristic hand positioning with overlapping fingers (clenched fists with the index finger overlapping the third and the fifth finger overlapping the fourth) is a hallmark finding. Congenital heart defects are present in over 90% of affected individuals, most commonly ventricular septal defects and polyvalvular disease. Other features include rocker-bottom feet, short sternum, renal malformations, omphalocele, and severe intellectual disability. Many affected pregnancies result in miscarriage or stillbirth. The prognosis for full trisomy 18 is very poor, with median survival of approximately 5 to 15 days. Approximately 50% of affected infants do not survive beyond the first week of life, and only 5–10% survive beyond the first year. Individuals with mosaic trisomy 18 may have a milder phenotype and longer survival. There is no cure for trisomy 18. Management is supportive and individualized, focusing on comfort care, nutritional support, and treatment of specific complications such as cardiac defects when appropriate. Palliative care discussions are an important component of management. Advanced maternal age is a recognized risk factor, and prenatal diagnosis is possible through screening tests and confirmatory procedures such as amniocentesis or chorionic villus sampling.

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